The syntax is incorrect, but yeah, you are on the right track. You still have to give your struct members datatypes! Also, You don't need to put in the "unused" 3 bit wide variable (unless you are planning on using it, , which i'm doubting from the name, or for some reason just want those 3 bits to be of a certain value). Your structure will automatically be padded, just like any other case.

Code:

struct Stuff
{
int var : 1,
var2 : 4,
unused : 3;
};

Also, it appears as though you want var to be used as a bool. You can declare it as a bool then!